research

Biology and pathology of turfgrass anthracnose Anthracnose is a serious disease of cool-season turf on golf courses, but new genetic tools and cultivar development may limit the disease.

Editor’s note: In the late 1990s and early 2000s, anthracnose disease and annual bluegrass weevils caused dramatic losses of annual bluegrass on putting greens in the northeastern United States. In response, in 2005, scientists from several universities formed the NE-1025 group to conduct research to solve problems related to these pests. As a result of the research, an initial set of best management practices was developed for anthracnose and control and published in GCM in August 2008. The research project was completed in 2011, and the researchers are now publishing additional information on best management practices for anthracnose control in the May and June issues of GCM. The first two articles in the series make up this month’s research section.

In the mid-1990s, anthracnose basal rot disease and cereal grain crops worldwide (3). Although emerged as one of the key management issues fac- numerous cool- and warm-season turfgrass hosts ing superintendents who maintain annual blue- are susceptible to anthracnose, the disease is most grass () putting greens. In this article, we damaging on annual bluegrass (Poa annua) and provide an updated overview of the biology, host creeping bentgrass ( stolonifera) maintained range, symptomology and epidemiological factors at putting green height. For reasons not fully under- influencing the pathology of anthracnose basal rot. stood, annual bluegrass is particularly susceptible to anthracnose, with stands of the grass severely dam- Host susceptibility aged when conditions are optimal for disease devel- Anthracnose is a common disease on grasses opment. Because anthracnose attacks weakened or

This research was funded in part by grants from the Environmental Institute for Golf and the USGA.

Jo Anne Crouch, Ph.D. Bruce B. Clarke, Ph.D. Anthracnose on the annual bluegrass putting green at Ridgewood CC, Paramus, N.J. Photo courtesy of P. Majumdar

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senescent turf, annual bluegrass is especially vul- cereale has been documented nerable when maintained under conditions of low in the United States for more than a century (7). mowing, low fertility or drought stress. The risk The was first described in 1908 from Ohio, of anthracnose infection to annual bluegrass turf where C. cereale was observed infecting several is further intensified during hot, humid weather. cool-season grasses, including Kentucky bluegrass, Anthracnose disease may also develop on other redtop (), orchardgrass (Dactylis cool-season turfgrass species such as fine fescues glomerata), and grain crops such as wheat (Triticum (Festuca species), Kentucky bluegrass (P. pratensis), aestivum) and rye (Secale cereale) (3). Anthracnose ryegrasses (Lolium species) and velvet bentgrass (A. of annual bluegrass was first diagnosed in 1928 canina), but is uncommon and rarely destructive from New Jersey, where C. cereale was observed on these grasses (7). Anthracnose also occurs on infecting roots and basal leaves (16). warm-season turfgrasses such as centipedegrass inhabits many environ- (Eremochloa ophiuroides) and bermudagrass (Cyn- ments outside of golf courses, including orna- odon dactylon) (6,15). mental grasses, residential , meadows, for- age grasses, prairies and natural grasslands (7). Anthracnose of cool-season turf Sporadic anthracnose disease outbreaks caused by The pathogen causing anthracnose disease in C. cereale occurred in wheat, cereal rye and oats cool-season grasses, the fungus Colletotrichum cere- (Avena sativa) during the first part of the 20th ale, inhabits temperate climate zones across the century, often in association with low fertility (3). United States, Canada, Western Europe, South Today, with the exception golf course turfgrass, C. America, Southeast Asia, New Zealand and Aus- cereale rarely triggers disease; however, the fungus tralia (3). Colletotrichum cereale, previously called is able to colonize other hosts without visibly affect- C. graminicola, closely resembles other Colletotri- ing health (7). chum fungi that cause anthracnose disease in corn, Even though C. cereale infects a wide range of sorghum, switchgrass, sugarcane and other mem- cool-season grasses, DNA fingerprint analysis of bers of the grass family. However, while C. cereale the fungus collected from cool-season grasses in and other grass anthracnose pathogens are related the United States, Canada, Japan, Australia and to each other, DNA fingerprint analysis shows they Europe has shown that individuals from different are unique organisms, each infecting entirely dif- host are members of 11 distinct population ferent hosts (4). groups (7). These populations are predominantly

Anthracnose symptoms on annual bluegrass putting green turf. Photo courtesy of B. Clarke

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divided according to host association. Only one of the 11 C. cereale populations includes individuals from both turfgrass and non-turfgrass hosts (for example, agronomic crop plants, native grasses, etc.). Most turfgrass strains of this pathogen pos- sess unique DNA fingerprints that separate them from C. cereale collected from other host plants. Additionally, DNA fingerprints from individuals of C. cereale infecting annual bluegrass are dissimilar from fingerprints of the fungus infecting creeping bentgrass. Anthracnose of warm-season turfgrasses Anthracnose in warm-season turfgrass is less common and less destructive than the disease that affects annual bluegrass and creeping bentgrass. Consequently, anthracnose has been poorly studied in warm-season turfgrasses. Recent DNA research has shown that anthracnose of warm-season turf- grasses is not caused by the same species of Colletot- richum that is responsible for disease in cool-season

Top: Anthracnose on centipedegrass turfgrass. Photo courtesy of M. Tomaso-Peterson Bottom: Colletotrichum cereale acervuli with setae on leaf sheath of annual bluegrass. Photo courtesy of L. Stowell

98 GCM May 2012 research turfgrass (C. cereale), although these fungi do share foliar infection between 81 F and 91 F (27.2 C and similarities in their appearance (5). Given the many 32.8 C) (8). anatomical, structural, metabolic and biochemical Colletotrichum cereale conidia are transported differences between cool-season and warm-season by wind and water, or mechanically through foot grasses, this finding is not surprising. The dissimi- trafffic, mowers or other equipment. Upon contact larity between the different anthracnose pathogens with a susceptible turfgrass plant, the conidia ger- may reflect adaptations to the unique hosts that minate within approximately two to six hours, and they infect. a structure called a germ tube is produced. Forma- Anthracnose of centipedegrass is caused by tion of the germ tube leads to the development of C. eremochloae, a newly discovered fungus that is a suction cup-like object called an appressorium, a a closely related sibling of the fungus responsible dark-brown, dome-shaped structure measuring for sorghum anthracnose, C. sublineola (6). Recent less than 0.01 inch (0.25 millimeter) in diameter. DNA fingerprinting of anthracnose fungi from Appressoria (plural of appressorium) adhere firmly preserved centipedegrass samples intercepted by to the host, allowing the fungus to penetrate the United States port authorities in 1923 indicates outer plant cuticle into the underlying tissue via a that C. eremochloae was likely introduced along penetration peg that forces its way into the plant with the host when it was first imported from using tremendous pressure. China during the early 20th century (6). Anthrac- Although this pressure has never been calcu- nose on zoysiagrass (Zoysia species) and bahiagrass lated for C. cereale, optical wave measurements (Paspalum notatum) is associated with C. caudatum have shown that a single appressorium from the and C. paspali in Japan, but it is unknown whether related corn pathogen C. graminicola is able to these fungi are present on these turfgrass hosts in exert forces up to 25 μN on host tissue (1). To put (3). The anthracnose pathogen of this in perspective, if a force of 17 μN were exerted bermudagrass is a species of Colletotrichum that has across the palm of a human hand, that individual not yet been identified. would be able to lift a school bus weighing almost 17,000 pounds (7.7 metric tons). The formation Symptomology, diagnosis and the of appressoria has been observed within six hours disease cycle after conidia make contact with leaves or stems, Host infection by the anthracnose fungus and penetration of host tissue may occur within Knowledge of anthracnose biology in turfgrass 24 hours (12). High humidity and/or extended is still incomplete. Nonetheless, several stages of periods of leaf wetness are critical during this time, the life cycle of Colletotrichum cereale are known, since desiccation of germinating condia will greatly and research from related Colletotrichum grass reduce the potential for infection. pathogens provides insight into how the infection process presumably works in annual bluegrass and bentgrass. Although anthracnose outbreaks sometimes occur on infected turfgrass in winter, the fungus is believed to be largely inactive during cold weather. Colletotrichum cereale is thought to survive harsh winter conditions as fungal mycelium in decaying plant residues or living host tissues. On oats and barley (Hordeum vulgare) crops, C. cereale survives the winter months by forming dormant resting structures called sclerotia on roots close to the soil surface, but this aspect of the fungal lifecycle has not been studied in turf (3). Colletotrichum cereale spreads from plant to plant through the movement of crescent-shaped, asexual reproductive spores called conidia. Warm weather, high humidity and high light intensity all serve to promote conidia formation. This is one of the reasons why anthracnose is so common in summer. Laboratory studies have shown that some Symptoms and signs of anthracnose basal rot on annual isolates of C. cereale grow best between 70 F and bluegrass. Photo courtesy of P. Landschoot 88 F (21.1 C and 31.1 C) and are able to cause

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Symptoms/diagnosis of anthracnose on easily pulled away from the crown. cool-season turf It is unknown how long it takes for symptoms Factors affecting disease severity to develop once Colletotrichum cereale conidia Scientists have observed that anthracnose first adhere to the surface of a susceptible host, is generally most destructive on weakened or and symptom expression may vary depending on senescent turf (15). During the past 10 years, environmental conditions. For example, in field research performed on annual bluegrass greens studies performed over consecutive years in New has provided data in support of this conclusion. Jersey, annual bluegrass turf exhibited symptoms Anthracnose may cause extensive injury when of basal rot anthracnose between five or 18 days turf is maintained at a low height of cut, when after inoculation with C. cereale conidia (10). fertility is low, or when the turfgrass is stressed Infection of leaf or stem tissue with C. cere- by abiotic factors such as drought or excessive ale results in the development of acervuli (repro- heat (10,11,13-15). However, contrary to earlier ductive bodies containing conidia) on the surface theories, data from recent field studies show that of the host tissue; these structures may become activities causing wounded tissue (for example, abundant as the disease progresses. Acervuli are foot traffic, rolling, double-cutting and verticut- cushion-like fruiting bodies composed of a mat of ting) do not appear to enhance the severity of fungal hyphae. Hyphae within acervuli give rise to anthracnose on turfgrass (10,11,13,14). two important structures: setae and conidia. Setae Consequently, although plant health and vigor are thin, tapering, black hair-like structures that have been demonstrated as major factors influenc- project from the acervuli; these structures are a ing disease severity, additional factors such as cul- key diagnostic feature of the anthracnose fungus tivar susceptibility, environment and variation in and can be easily detected using a hand lens. The pathogen populations may also play a role in dis- acervuli are also the primary site of conidia pro- ease development. In particular, variable response duction, and as such provide a source of future to anthracnose has recently been documented on infections. cultivars and experimental selections of creeping Conidia within the acervuli are suspended in and velvet bentgrass (2). Anthracnose response a sticky liquid that serves to protect the conidia from commercial cultivars of creeping bentgrass from drying, prevents the conidia from premature evaluated at Rutgers University ranged from very germination, and may aid the fungus in initiating good disease tolerance (Shark, Penneagle II, Run- infection (3). When acervuli are splashed with ner, Penn A-1, Tyee and Authority) to highly sus- water, this liquid is diluted, germination inhibi- ceptible (Viper, Providence, Penncross, Brighton, tors are broken down, conidia are moved to fresh Seaside II and Pennlinks II) (2). Similar research new host tissue, and the disease cyle begins anew. is ongoing with annual bluegrass, with certain Anthracnose is most severe during warm, clones and selections being developed at Penn humid weather. Nonetheless, outbreaks may State University that show improved tolerance to occur throughout the year, causing either a foliar anthracnose disease (9). blight or a basal rot of leaf sheaths, crowns and stolons (15). Both basal rot and foliar blight symp- Future research toms are favored by high temperatures (85 F-95 F; Much remains to be learned about the anthrac- 29.4 C-35 C ) and may be present simultaneously nose infection process and how differences across on annual bluegrass, especially when turf is under diverse populations of Colletotrichum cereale may heat stress. affect disease severity and control on golf course Anthracnose symptoms on cool-season turf- putting greens. Progress in this area has been hin- grasses vary based on the host plant. Symptoms dered by the lack of a reliable greenhouse inocu- on annual bluegrass initially emerge as yellow- lation procedure. Field inoculations have been to orange-colored spots between 0.25 and 0.5 sucessfully employed to evaluate the impact of inch (0.64-1.27 centimeters) in diameter (15). management factors on anthracnose severity, On creeping bentgrass, infected foliage becomes resulting in the development of an evolving set orange or red to reddish brown. If left uncon- of best management practices that have benefited trolled, spots coalesce, forming large, irregular superintendents throughout the world (see the areas of blighted turf. Older or senescent leaves companion articles in this issue and in the June may be among the first colonized by the fungus. 2012 GCM). Infection of leaves close to the soil surface in close- Development of a reliable greenhouse inocula- cut turf often results in a characteristic “basal rot” tion protocol will facilitate valuable investigations symptom, where water-soaked, blackened tissue is of turfgrass anthracnose disease under controlled

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environments, including dissections of the infection 7. Crouch, J.A., L.P. Tredway, B.B. Clarke and B.I. Hillman. cycle, pathogenicity testing, screening of turfgrass 2009. Phylogenetic and population genetic divergence cor- cultivars for anthracnose resistance and experimen- respond with habitat for the pathogen Colletotrichum cereale tal studies of the factors influencing host-pathogen and allied taxa across diverse grass communities. Molecular interactions. Moreover, the use of an increasingly Ecology 18:123-135. powerful and rapidly expanding set of DNA and 8. Danneberger, T.K., J.M. Vargas Jr. and A.L. Jones. 1984. genetic tools, including DNA sequencing of sev- A model for weather-based forecasting of anthracnose on eral anthracnose pathogen genomes, is continuing annual bluegrass. Phytopathology 74:448-451. to enhance our ability to study and identify the 9. Huff, D.R. 2004. Developing annual bluegrass cultivars for mechanisms involved in the infection process and putting greens. USGA Turfgrass and Environmental Research the suppression of anthracnose through improved Online (May 1) 3(9):1-8. management practices. This should also speed up 10. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2008. Anthrac- new cultivar development by allowing breeders to nose severity on annual bluegrass influenced by nitrogen fer- identify and screen all of their turfgrass selections tilization, growth regulators, and verticutting. Crop Science for anthracnose-resistance genes before even step- 48:1595-1607. ping foot into the field. The knowledge gained 11. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2009. Anthrac- from this type of research will greatly enhance our nose disease and annual bluegrass putting green perfor- understanding of anthracnose and the ability of mance affected by mowing practices and lightweight rolling. superintendents to control this devastating disease Crop Science 49:1454-1462. in the future. 12. Khan, A., and T. Hsiang. 2003. The infection process of Col- V letotrichum graminicola and relative aggressiveness on four Funding turfgrass species. Canadian Journal of Microbiology 49:433- v The authors thank the United States Department of Agri- 442. v culture (USDA) Agricultural Research Service, USDA Multistate 13. Roberts, J.A. 2009. Impact of cultural management on Research Projects NE-1025 and NE-1046, the Environmental anthracnose severity of annual bluegrass putting green turf. The research says Institute for Golf, GCSA of New Jersey, New Jersey Turfgrass M.S. thesis, Rutgers University, New Brunswick, N.J. Association, Tri-State Turf Research Foundation, United States 14. Roberts, J.A., J.C. Inguagiato, B.B. Clarke and J.A. Murphy. ➔ Anthracnose is a serious Golf Association, the U.S. Department of Energy/Joint Genome 2011. Irrigation quantity effects on anthracnose disease of disease of annual bluegrass and Institute and the Rutgers Center for Turfgrass Science for sup- annual bluegrass. Crop Science 51:1244-1252. creeping bentgrass, but knowledge porting this work. A portion of the research described in this 15. Smiley, R.W., P.H. Dernoeden and B.B. Clarke. 2005. Com- of anthracnose biology in turf is still paper has been funded by the USDA. Mention of a trademark pendium of Turfgrass Diseases. 3rd ed. APS Press, St. Paul, incomplete. name or proprietary product does not constitute a guarantee by Minn. ➔ Anthracnose is most severe the USDA. 16. Sprague, H.B., and E.E. Evaul. 1930. Experiments with turf- during warm, humid weather, but grasses in New Jersey. New Jersey Agricultural Experiment outbreaks may occur throughout Literature cited Station Bulletin 497:1-55. 1. Bechinger, C., K.F. Giebel, M. Schnell et al. 1999. Optical the year. GCM ➔ Anthracnose is most measurements of invasive forces exerted by appressoria of plant pathogenic fungi. Science 285:1896-1899. destructive on weakened or senes- Jo Anne Crouch ([email protected]) is a research 2. Bonos, S.A., E.N. Weibel, T.J. Lawson and B.B. Clarke. 2009. cent turf; low fertility, low mowing molecular biologist at the U.S. Department of Agriculture− heights, drought and excessive heat Tolerance of creeping bentgrass cultivars and selections to Agricultural Research Service, Systematic Mycology and enhance the disease. anthracnose in New Jersey. Online. Applied Turfgrass Science Microbiology, Beltsville, Md., and Bruce B. Clarke is director of ➔ Activities causing wounded doi:10.1094/ATS-2009-0806-01-BR. the Center for Turfgrass Science and an Extension specialist in the department of plant biology and pathology at Rutgers tissue do not appear to enhance the 3. Crouch, J.A., and L.A. Beirn. 2009. Anthracnose of cereals University, New Brunswick, N.J. severity of anthracnose on annual and grasses. Fungal Diversity 39:19-44. bluegrass putting greens. 4. Crouch, J.A., B.B. Clarke and B.I. Hillman. 2006. Unraveling ➔ Cultivar susceptibility, envi- evolutionary relationships among the divergent lineages of ronment and variation in pathogen Colletotrichum causing anthracnose disease in turfgrass and populations may play a role in dis- corn. Phytopathology 96:46-60. ease development. 5. Crouch, J.A., B.B. Clarke, J.F. White Jr. and B.I. Hillman. 2009. Systematic analysis of the falcate-spored graminico- lous Colletotrichum and a description of six new species of the fungus from warm-season grasses. Mycologia 101:717-732. 6. Crouch, J.A., and M. Tomaso-Peterson. 2012. Anthracnose disease of centipedegrass turf caused by Colletotrichum ere- mochloae, a new fungal species closely related to Colletotri- chum sublineola. Mycologia doi:10.3852/11-317.

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Best management practices for anthracnose on annual bluegrass Using the correct cultural practices can lessen the severity of anthracnose disease on annual bluegrass.

Anthracnose (caused by Colletotrichum cere- prehensive set of best management practices for ale) is a destructive fungal disease that can destroy the control of anthracnose disease on golf courses. weakened turf and is particularly severe on annual bluegrass (Poa annua). It occurs throughout the Nitrogen fertility United States, Canada and Western Europe (19) Soluble nitrogen as well as Australia and Japan (2). Outbreaks of Management of nitrogen fertility is crucial anthracnose on golf course putting greens started to maintaining the health and vigor of the turf, to increase in frequency and intensity during the which, in turn, affects playability (“speed” and mid-1990s (4,5,10,11). Since then researchers have smoothness of ball roll) on putting greens. Initial determined that the severity of anthracnose is research clearly indicated that applying soluble influenced by many of the management practices nitrogen (0.1 pound/1,000 square feet [4.9 kilo- used by superintendents. grams/hectare]) on a seven-day schedule from Scientists within the NE-1025 multi-state turf late spring through summer reduces anthracnose research project have reported their initial find- severity up to 24% compared to applying the ings of how annual bluegrass management prac- same nitrogen rate every 28 days (5). tices affect anthracnose disease (16). That report The exact reason(s) for reduced anthracnose addressed the effects of nitrogen fertility, chemi- severity in plants receiving greater nitrogen nutri- This research was funded in part by the cal growth regulation, mowing, rolling, topdress- tion are not known, but improved plant vigor United States Golf Association and the ing, verticutting and irrigation on anthracnose of has been proposed (23). More recently, research- Environmental Institute for Golf. annual bluegrass putting green turf. This report ers have discovered that frequent soluble nitro- updates our conclusions on these practices since gen fertilization reduces anthracnose severity as 2008. These results are being used to revise a com- the nitrogen rate increases up to the equivalent

James Murphy, Ph.D. John Inguagiato, Ph.D. Bruce Clarke, Ph.D. Anthracnose on annual bluegrass (basal rot and black acervuli on lower stem, left, and severe thinning associated with the disease on a golf course putting green, right). Photos by J. Roberts

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of 0.2 pound/1,000 square feet/week (9.8 kilo- Nitrogen is applied with a spray hawk to evaluate the impact of different nitrogen grams/hectare/week) (15). In fact, short-term use sources and rates on anthracnose. of nitrogen at rates of 0.4-0.5 pound/1,000 square Photo by J. Murphy feet/week (19.5-24.4 kilograms/hectare/week) applied before disease symptoms become severe are very effective at reducing anthracnose sever- [≥73.2 kilograms/hectare]) than spring applica- Fall applications of granular nitrogen ity. However, if these high rates are continued into tions (13,14). Thus, superintendents with a his- fertilizer (top) are not as effective as spring applications (bottom) in reduc- the summer, disease severity increases dramati- tory of anthracnose on their putting greens need ing anthracnose severity of annual cally (14,15). to re-evaluate the common practice of late-season bluegrass turf. Photos by C. Schmid A recent trial conducted to assess the effect nitrogen fertilization because it is not an efficient of soluble nitrogen source on anthracnose sever- or cost-effective tactic for managing anthracnose ity of annual bluegrass putting green turf showed disease on annual bluegrass turf. Superintendents that potassium nitrate reduced disease severity, should strongly consider shifting more of their whereas weekly applications of ammonium sulfate granular nitrogen from the fall to the spring if increased anthracnose compared to urea, ammo- their program is currently weighted toward the nium nitrate and calcium nitrate (15). Follow-up fall. trials were initiated in 2011 to specifically assess Scientists have further observed that, despite the effect of potassium fertilization and soil pH the positive effects of spring fertilization with on anthracnose. Further research is needed to con- granular nitrogen, frequent soluble nitrogen appli- firm and clarify the first-year observations in these cations are also needed through the summer to trials, but it appears that potassium deficiency adequately suppress late-summer symptoms of may increase the severity of this disease. Greater anthracnose. Thus, best management practices soil acidity reduced the vigor of annual bluegrass, for nitrogen fertilization include an emphasis on but it was not clear how much impact it had on granular nitrogen fertilization from early to mid- anthracnose severity. spring (1-2 pounds/1,000 square feet [48.8-97.6 kilograms/hectare], possibly more under severe Granular nitrogen disease pressure), and frequent low-rate soluble Similar to previous results with soluble nitro- nitrogen from late spring through summer (up to gen, research on granular nitrogen (slow-release) 0.2 pound/1,000 square feet every seven days). has shown that applying higher rates of nitro- gen in spring before anthracnose becomes severe Topdressing practices reduces anthracnose severity. Interestingly, while Initial speculation frequently suggested that slow-release granular nitrogen applied in the fall sand topdressing would contribute to anthrac- can reduce disease severity the next growing sea- nose epidemics on putting greens. Although son, this tactic requires considerably more nitro- researchers have observed that sand topdressing gen (1.5 pounds or more per 1,000 square feet may slightly increase disease when applications

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ity, with spring being the most beneficial time of application. Therefore, it would be best for super- intendents to implement an aggressive topdressing program (for example, 400-800 pounds/1,000 square feet [19.5-39 metric tons/hectare]) in spring, especially if it is not feasible to make fre- quent, moderate-rate topdressing applications during the summer. This research also indicates that superintendents should not forgo spring top- dressing even if they implement an aggressive fall topdressing program. Although fall topdressing is beneficial, its positive effects on anthracnose do not last as long into the summer as those of spring topdressing, especially when summer topdressing is limited. Irrigation management Turf growing in saturated soil caused by poor surface drainage and slow internal drainage is more susceptible to anthracnose than turf that is not overwatered (20,22). In addition, research conducted in a growth chamber indicates that annual bluegrass plants subjected to drought stress before inoculation exhibit greater anthrac- Routine applications of sand top- are made at insufficient rates and/or intervals, this nose disease (3). Field research has now confirmed dressing at appropriate rates can effect contrasts with the significant reduction in that drought stress increases anthracnose severity significantly reduce anthracnose on annual bluegrass (18). Specifically, irrigation severity. Photo by R. Wang disease severity that occurs with routine applica- tions of sand at appropriate rates. Research has regimes that subject turf to frequent wilt stress consistently confirmed that aggressive programs during warm, dry weather (that is, less than 60% involving frequent, moderate-rate topdressing ETo) will increase anthracnose disease. Moreover, (100 or 200 pounds/1,000 square feet [4.9-9.8 overwatering turf (100% ETo) often results in metric tons/hectare] every seven or 14 days) sub- increased anthracnose severity by the end of the stantially reduce anthracnose during the grow- summer. Superintendents should manage irriga- ing season (9,12). Moreover, the beneficial effect tion to minimize drought stress (that is, irrigating of sand topdressing has been proved to hold true at 60%-80% ETo) while implementing practices under conditions of intense foot traffic (that is, the that prevent saturated soil conditions to reduce equivalent of 200 rounds per day) with golf shoes anthracnose on putting greens. fitted with soft spikes (12). A study examining the method of sand incor- Verticutting poration (stiff- vs. soft-bristled brush, vibratory Verticutting is used on putting greens to mini- rolling or none) showed no effect on anthracnose. mize puffiness (improve surface playability) and Moreover, sand particle shape (round vs. sub- other problems associated with thatch accumu- angular) had little effect on disease severity, but, lation. Although verticutting has been reputed when a difference was observed, disease severity to enhance anthracnose by wounding host plant was lower in plots topdressed with sub-angular tissue (4,10,19), research has not confirmed such sand (unpublished data). speculation (5). Recent detailed studies examin- Summer sand topdressing has proved to be ing the potential impact of mechanical injury (ver- very successful at reducing anthracnose severity, ticutting, coring and solid tining) on anthracnose yet superintendents have substantial challenges while the disease was active indicate that wound- that limit the implementation of an aggressive ing of leaves, crowns or stolons does not increase topdressing program during mid-season. As a anthracnose severity on annual bluegrass putting result, researchers have more recently examined greens (15). Thus, superintendents should not be the impact of spring and fall topdressing pro- overly concerned about cultivation (verticutting, grams on anthracnose (15). Findings from this coring and solid tining) programs contributing research indicate that fall and spring applications to anthracnose disease problems. In fact, a well- are also effective at reducing anthracnose sever- designed and properly implemented cultivation

106 GCM May 2012 research program should benefit an anthracnose manage- ment plan by creating an environment that sup- ports healthy turf growth. Mowing and rolling Research has shown that low cutting height has a greater effect on anthracnose severity on putting greens than any other part of a mowing and rolling program. Low cutting heights will increase anthracnose severity (1,19), whereas more frequent mowing (double cutting) has no effect on this disease (6). It was formerly speculated that double cutting would intensify anthracnose by wounding leaf tissue but, as discussed above, recent mechanical injury studies have not sup- ported this theory. Similarly, lightweight rolling, used to smooth the turf canopy and improve ball roll, was thought to increase stress and susceptibil- ity to anthracnose on putting greens, but research (either with a vibratory or sidewinder unit per- formed every other day) indicates this practice either has no effect or slightly reduces the severity of this disease (6,13,14,17). A study assessing the impact of additional traf- fic caused by the change of direction from roll- ing equipment and clean-up mowing along the perimeter of putting greens showed no intensifica- tion of anthracnose (12,17). Thus, any incidence of greater anthracnose severity at the perimeter of putting green is likely due to other factors. To improve anthracnose management, super- tion (8). However, more research on the interac- Top: Verticutting was not found to increase anthracnose severity intendents should favor a mowing and rolling tion of PGRs and nitrogen nutrition is needed to on annual bluegrass putting program that avoids reducing the mowing height gain better insight into this matter. Superinten- greens. Photo by R. Miller (for example, not less than 0.125 inch [3.2 milli- dents should continue to use PGRs to enhance meters]) and adopts the practices of either double turf quality and playability of annual bluegrass Bottom: Anthracnose disease severity was rated on test plots cutting and/or rolling to improve playability (ball turf without concern that they might enhance as part of the research carried roll). anthracnose severity. out at Rutgers University. Photo by J. Hempfling Plant growth regulators Summary Many superintendents use plant growth reg- Best management practices for the control ulators (PGRs) to manage golf course turfgrass. of anthracnose disease on annual bluegrass turf Growth regulators commonly used to enhance include adequate nitrogen fertilization in early annual bluegrass turf include Embark (mefluid- spring followed by a frequent low-rate nitro- ide, PBI/Gordon) and Proxy (ethephon, Bayer), to gen fertility program initiated in late spring and regulate seedhead development, and Primo Maxx continued through summer. Granular nitrogen (trinexapac-ethyl, Syngenta) to improve shoot rates of 1 to 2 pounds/1,000 square feet in early density and reduce shoot elongation. As stated in to mid-spring combined with frequent, soluble our previous GCM article, studies have not dem- nitrogen applied at 0.1 to 0.2 pound/1,000 square onstrated any consistent effects of these PGRs on feet/week in late spring and summer will be help- anthracnose disease (16). ful in reducing anthracnose severity. Two recent studies examining the use of these An aggressive topdressing program during the PGRs alone or in combination indicate that, spring is particularly important if it is not feasi- although they do not intensify anthracnose as ble to implement a frequent program of moder- was previously speculated, they can reduce dis- ate topdressing during the summer. Although fall ease severity in some cases (7,8). In fact, research topdressing can be important for other reasons, suggests that PGR use may contribute to anthrac- superintendents need to realize that its positive nose suppression by enhancing nitrogen nutri- effects on anthracnose will not last as long into

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BMPs for anthracnose on annual bluegrass greens

Nitrogen Irrigation • Apply nitrogen to maintain vigor of the putting green turf • Increased anthracnose can result when annual bluegrass without overfertilizing. is consistently subjected to wilt stress or excessively wet • Apply granular nitrogen fertilization at rates of 1-2 conditions. pounds/1,000 square feet (48.8-97.6 kilograms/hectare) in • Irrigating to replace 60%-80% of reference evapotranspira- spring (rather than fall) to reduce disease severity. Nitrogen tion and hand watering as needed to avoid wilt stress will rates up to 3.0 pounds/1,000 square feet (146.5 kilograms/ provide high-quality playing conditions and reduce condi- hectare) in spring effectively suppress anthracnose but are tions favorable for anthracnose. recommended only if the historical disease pressure has been severe. At higher rates, include slow-release nitrogen as Mowing and rolling part of the fertilizer to extend the response and avoid a surge • Mowing below 0.125 inch (3.2 millimeters) should be in growth. avoided whenever possible. If feasible, raise the cutting • Begin summer nitrogen programs earlier in the year to height as high as 0.141 inch (3.6 millimeters) for greater allow nitrogen buildup in the turf, which will decrease suppression of anthracnose. Slight increases in mowing anthracnose severity. In summer, apply a cumulative solu- height can significantly reduce disease severity. ble nitrogen rate of 1.5-3.0 pounds nitrogen/1,000 square • To maintain acceptable ball roll distances (~10 feet [3 feet (73.2-146.5 kilograms/hectare) to reduce anthracnose meters]) at higher mowing heights, roll and/or increase severity. A program using a higher rate over summer will mowing frequency. Rolling, regardless of roller type, and likely need less nitrogen in the spring; a higher spring rate double cutting increase ball roll but will not enhance the is recommended if anthracnose is historically a problem in disease. mid- to late spring. • Rolling every other day may slightly reduce anthracnose severity. Topdressing • Sand topdressing applied every 7 days at 100 pounds/1,000 Plant growth regulators square feet or every 14 days at 200 pounds/1,000 square • Routine Primo Maxx (trinexapac-ethyl) use even at high feet (4.9 or 9.8 metric tons/hectare) provides a protective rates and short intervals does not increase anthracnose layer of sand around the crown, slightly raising the effective severity. Benefits of improved turf tolerance to low mowing height of cut and thus reducing anthracnose. and enhanced plant health may help reduce disease in some • Anthracnose is not affected by sand incorporation tech- cases. niques; select methods that best incorporate sand yet mini- • Embark (mefluidide) and Proxy (ethephon) can be used to mize turf injury and wear on mowing equipment. suppress seedhead formation in annual bluegrass without • Foot traffic on turf topdressed with sand reduces disease sever- increasing anthracnose. ity. Areas that receive daily foot traffic and sand topdressing • Embark or Proxy applied in March or April at label rates will have better wear tolerance and decreased disease. with subsequent applications of Primo Maxx at 0.125 fluid • Implement an aggressive topdressing program (for exam- ounce/1,000 square feet (0.40 liter/hectare) every seven to ple, 400-800 pounds/1,000 square feet [19.5-39 metric 14 days, or 0.1 fluid ounce/1,000 square feet (0.32 liter/ tons/hectare]) in spring; apply rates at the higher end of hectare) every seven days will provide the best turf quality this range if summer topdressing is not feasible. Spring top- and may reduce anthracnose. dressing is more effective at reducing anthracnose severity than fall topdressing.

Table 1. Best management the summer as spring topdressing, so thorough either double cutting and/or rolling to improve practices for anthracnose spring topdressing is essential. playability (ball roll). Superintendents should also disease on annual bluegrass putting green turf. Deficit irrigation is important to maintain avoid reducing the mowing height to improve playability and conserve water, but it must be anthracnose management. managed to avoid subjecting the turf to frequent Chemical growth regulation with Embark, episodes of wilt stress. In a successful deficit irriga- Proxy and Primo Maxx should not intensify and, tion program, routine monitoring of turf and soil in some cases, may reduce disease severity. water content are essential to ensure the accurate detection of threshold conditions that precede wilt Funding stress and trigger the decision to apply water. The authors thank the United State Department of Agriculture Mowing and rolling programs should include Multistate Research Projects NE-1025 and NE-1046, the Envi-

108 GCM May 2012 research

ronmental Institute for Golf, GCSA of New Jersey, the Tri-State grass and Environmental Research Summary. USGA Turf- Turf Research Foundation, the United States Golf Association and grass and Environmental Research Online 7(23):5. http:// the Rutgers Center for Turfgrass Science for the financial support turf.lib.msu.edu/ressum/2008/5.pdf. of this work. 13. Murphy, J.A., B.B. Clarke, J.A. Roberts et al. 2009. Devel- opment of best management practices for anthracnose dis- Acknowledgments ease on annual bluegrass putting green turf. In: 2009 USGA The authors acknowledge the contributions of Joseph A. Turfgrass and Environmental Research Summary. USGA Roberts, Charles J. Schmid, James W. Hempfling, Ruying Wang, Turfgrass and Environmental Research Online 8(23):4. the New Jersey Turfgrass Association and the New Jersey Agri- http://turf.lib.msu.edu/ressum/2009/4.pdf. cultural Experiment Station. 14. Murphy, J.A., B.B. Clarke, J.A. Roberts et al. 2010. Devel- opment of best management practices for anthracnose dis- Literature cited ease on annual bluegrass putting green turf. In: 2010 USGA 1. Backman, P., G. Stahnke and E. Miltner. 2002. Anthracnose Turfgrass and Environmental Research Summary. USGA update: Cultural practices affect spread of disease in north- Turfgrass and Environmental Research Online 9(23):2. west. Turfgrass Trends 11:T1-T2, T4. http://turf.lib.msu.edu/ressum/2010/2.pdf. 2. Crouch, J.A., B.B. Clarke and B.I. Hillman. 2006. Unraveling 15. Murphy, J.A., B.B. Clarke, C.J. Schmid et al. 2011. Devel- evolutionary relationships among the divergent lineages of opment of best management practices for anthracnose dis- Colletotrichum causing anthracnose disease in turfgrass and ease on annual bluegrass putting green turf. In: 2011 USGA corn. Phytopathology 96:46-60. Turfgrass and Environmental Research Summary. USGA 3. Danneberger, T.K., J.M. Vargas Jr. and A.L. Jones. 1984. Turfgrass and Environmental Research Online 10(23):2. V A model for weather-based forecasting of anthracnose on http://turf.lib.msu.edu/ressum/2011/2.pdf. v annual bluegrass. Phytopathology 74:448-451. 16. Murphy, J., F. Wong, L. Tredway et al. 2008. Best manage- 4. Dernoeden, P.H. 2002. Creeping bentgrass management: ment practices for anthracnose on annual bluegrass turf. v summer stresses, weeds, and selected maladies. John Wiley Golf Course Management 24:93-104. & Sons, Hoboken, N.J. 17. Roberts, J.A., B.B. Clarke and J.A. Murphy. 2012. Light- The research says 5. Inguagiato, J.C, J.A. Murphy and B.B. Clarke. 2008. weight rolling effects on anthracnose of annual bluegrass Anthracnose severity on annual bluegrass influenced by putting greens. Agronomy Journal (in press). ➔ Provide adequate nitrogen fer- nitrogen fertilization, growth regulators, and verticutting. 18. Roberts, J.A., J.C. Inguagiato, B.B. Clarke and J.A. Murphy. tilization in early spring, initiate frequent Crop Science 48:1595-1607. 2011. Irrigation quantity effects on anthracnose disease of low-rate nitrogen fertility in mid- to late 6. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2009a. annual bluegrass. Crop Science 51: 2044-1252. spring and continue through summer. Anthracnose disease and annual bluegrass putting green 19. Smiley, R.W., P.H. Dernoeden and B.B. Clarke. 2005. Com- ➔ If frequent moderate topdress- performance affected by mowing practices and lightweight pendium of turfgrass diseases. 3rd ed. APS Press, St. Paul, ing is not feasible in summer, aggressive rolling. Crop Science 49:1454-1462. Minn. topdressing in spring is essential. 7. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2009b. 20. Sprague, H.B., and E.E. Evaul. 1930. Experiments with turf- ➔ Fall topdressing will not replace Anthracnose of annual bluegrass putting green turf influ- grasses in New Jersey. New Jersey Agricultural Experiment spring topdressing for anthracnose enced by trinexapac-ethyl application interval and rate. Jour- Station Bulletin 497:1–55. control. nal of the International Turfgass Society 11:207-218. 21. Uddin, W., M.D. Soika and E.L. Soika. 2006. Influence of ➔ Deficit irrigation must avoid 8. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2010. nitrogen source and rate on severity of anthracnose basal subjecting the turf to frequent episodes Anthracnose development on annual bluegrass affected by rot in mixed annual bluegrass and creeping bentgrass of wilt stress. seedhead and vegetative growth regulators. Applied Turf greens. Phytopathology 93:S86. ➔ Use double cutting and/or rolling Science DOI:10.1094/ATS-2010-0923-01-RS. 22. Vargas, J.M., and A.J. Turgeon. 2003. Poa annua: physiol- to improve playability, avoid reducing the 9. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2012. Sand ogy, culture, and control of annual bluegrass. John Wiley & mowing height to improve anthracnose topdressing rate and interval effects on anthracnose severity Sons, Hoboken, N.J. management. of an annual bluegrass putting green. Crop Science 52(3): 23. White, D.G., R.G. Hoeft and J.T. Touchton. 1978. Effect of ➔ Chemical growth regulation with (in press). nitrogen and nitrapyrin on stalk rot, stalk diameter, and yield Embark, Proxy and Primo Maxx should 10. Landschoot, P., and B. Hoyland. 1995. Shedding some light of corn. Phytopathology 68:811-814. not intensify disease severity and may on anthracnose basal rot. Golf Course Management 11:52- reduce it. 55. GCM 11. Mann, R.L., and A.J. Newell. 2005. A survey to determine James Murphy ([email protected]) is an Extension the incidence and severity of pests and diseases on golf specialist in turfgrass management and Bruce Clarke is director course putting greens in England, Ireland, Scotland, and of the Center for Turfgrass Science and an Extension specialist Wales. International Turfgrass Society Research Journal in turfgrass pathology in the department of plant biology and 10:224-229. pathology at Rutgers, The State University of New Jersey, 12. Murphy, J. A., B.B. Clarke and J.A Roberts. 2008. Develop- New Brunswick. John Inguagiato is an assistant professor in ment of best management practices for anthracnose disease turfgrass pathology in the department of plant science and landscape architecture at the University of Connecticut, Storrs. on annual bluegrass putting green turf. In: 2008 USGA Turf-

110 GCM May 2012 cutting edge Research in progress

ously, a replicated field trial was planted in 2011 for 15 of the fine-textured seeded families to evaluate their turf quality in 2012. This work is funded by the USGA. — A. Dennis Genovesi, Ph.D. (d-genovesi@ tamu.edu), and Ambika Chandra, Ph.D., Texas AgriLife Research Center-Dallas, Texas A&M University

Photo by A. Chaves Bacterial wilt of creeping bentgrass Bacterial wilt of bentgrass, caused by Acidovo- rax avenae (presumably variety avenae), is widely distributed throughout the United States, where it causes a wilt and decline of creeping bentgrass. In the growth chamber, A. avenae isolates were fully pathogenic on several creeping bentgrass cul- tivars and colonial and velvet bentgrass, moder- ately affected annual ryegrass, and did not attack Photo courtesy of M. Fidanza annual bluegrass or other turf-type grasses. Disease Fairy ring management depends on weather conditions and health of the The causal organism for fairy ring may vary turf. Highly stressed turf (e.g, golf course turf) because multiple fungi cause the disorder. In 2011, under high temperatures is most likely to be dam- the first year of a three-year study, 17 chemical and aged. No chemical pesticides are currently labeled cultural treatments, including untreated healthy for control of the disease. Growth chamber studies turf and untreated turf with fairy ring, were evalu- showed that Daconil Action (acibenzolar-S-methyl ated for suppression of active fairy ring on a golf + chlorotalonil, Syngenta) is effective at limiting course in Barrington, Ill. On July 18, treatments disease symptoms when applied preventively, and were applied and watered-in. Treatments were rated Primo Maxx (trinexapac-ethyl, Syngenta) does not for visual quality (1-9) and color intensity (0-4), appear to increase disease symptoms. This work is and Normalized Difference Vegetation Index was funded by the USGA. — Nathaniel Mitkowski, Ph.D. taken. There were no significant differences in ([email protected]), University of Rhode Island visual quality or NDVI on any date, and no phy- totoxicity occurred. On July 23, fairway flooding Seeded zoysiagrass ended the aggressive outbreak of fairy ring, which This research focuses on the development of did not return. This work is funded by the USGA. seeded zoysiagrass cultivars that are genetically — Michael Fidanza, Ph.D. ([email protected]), Pennsyl- stable with improved turf quality, high seed yields, vania State University; Derek Settle, Ph.D., Chicago Dis- persistence and competitive ability. In 2000, inter- trict Golf Association; Henry Wetzel, Ph.D., Sustainable specific hybrids of Zoysia japonica and Z. matrella Pest Management were made, yielding 1,600 progeny. After a two- year grow-in period, 53 lines were selected, 19 of GCM which were fine-textured. The focus is on fine tex- ture, seedhead production (density and height), Teresa Carson ([email protected]) is GCM’s science editor.

Photo by A.D. Genovesi turf quality and flowering time. Progeny derived from the fine-texture class seed parents have been advanced to a spaced plant nursery in 2011 for Teresa Carson another cycle of a recurrent selection. Simultane-

112 GCM May 2012